Many of the procedures of oilfield well servicing require that fluids and gases mixed with various chemicals and proppants be pumped down the oil or gas well (henceforth called the well) tubing or casing under high pressures during the operations called acidizing and fracturing. These operations serve to ready the well for production or enhance the present production of the well. The components which make up the wellhead such as the valves, tubing hanger, casing hanger, casing head and also the blow out preventer equipment generally supplied by the well servicing company, are usually sized for the characteristics of the well and are not capable of withstanding the fluid pressures at which these operations of fracturing and acidizing are carried out. There are wellhead components available to withstand high pressures, but it is not economical to equip every well with them. There are many tools which are in use in the field which allow these high pressure fluids and gases to bypass the wellhead components and these tools are generally referred to as wellhead isolation tools or in oilfield terms, tree savers, casing savers and top mounted packers. Some of the most popular in use today would include the inventor's tools; McLeod, a Wellhead Isolation Tool, Canadian Patent No. 1,217,128, U.S. Pat. No. 4,657,075 this tool being used to isolate the wellhead from pressure in the casing; McLeod, a Well Casing Packer, Canadian Patent No. 1,232,536, U.S. Pat. No. 4,691,770, this tool being used to isolate wellhead equipment from pressure in the casing or tubing, depending on which it is set into; McLeod, a Wellhead Isolation Tool, U.S. Pat. No. 4,991,650, this tool being used to isolate wellhead equipment from pressure in the casing or tubing, depending on which it is set into; Bullen, a Well Tree Saver, Canadian Patent No. 1,094,945, this tool being used to isolate the wellhead array from pressure in the tubing; Cummins (Assigned to Halliburton Co.) a Wellhead Isolation Tool and Method of Use Thereof, U.S. Pat. No. 3,830,304, this tool being used to isolate the wellhead array from pressure in the tubing. Oliver (Assigned to Halliburton Co.) Wellhead Isolation Tool, U.S. Pat. No. 4,111,261, showing a tool much like the Cummins Patent but including a nipple system for the mandrel; Sutherland-Wenger, a Wellhead Isolation Tool Nipple, Canadian Pat. No. 1,272,684. This shows a nipple on a mandrel which is moved into the wellhead by a concentric telescoping cylinder; Dallas et al, A Wellhead Isolation Tool and Method of Using Same, Canadian Patent No. 1,267,078, U.S. Pat. No. 4,867,243 which shows a removable cylinder moving a mandrel into the wellhead. There are many other tools operating on the same principle; to insert a mandrel with a sealing nipple on the lower end through the wellhead and into the tubing or casing below the wellhead, thus isolating the wellhead from the pressure and fluid being pumped into the tubing or casing.
The isolation tools in general use have the following drawbacks.
1. During the insertion of the mandrel into the wellhead with the isolation tools proposed by McLeod, Bullen, Dallas et al and others, the wellhead valves are open and if there were to be damage to the mandrel or a leak to occur in the mandrel packing of the isolation tool, there is the great possibility of the well blowing out with the attendant danger to personnel and environment.
Thus for example, referring to FIG. 2 of Canadian patent no. 1,267,078 of Dallas et al, when the mandrel 24 is inserted into the wellhead, the valves 11A and 11B will be open. If there is a leak in the mandrel packing (see FIG. 2b, element 22), well fluids could pass between the mandrel and the wellhead fittings, between the mandrel and the flange 20 and into the environment thus potentially causing an uncontrollable blowout.
2. The isolation tools described by McLeod (U.S. Pat. No. 4,991,650), Sutherland-Wenger and others, use a combination pressure chamber and hydraulic cylinder to protect the mandrel or confine any leaks through mandrel packing. (Those of Cummins and Oliver protect only a portion of the mandrel during operation.) This does confine any possible blowout, but due to the construction of the pressure chamber and hydraulic cylinder, the isolation tool assembly is very high and the attachment to the well servicing equipment is far above the ground.
For example, referring to FIGS. 2A, 2B and 3 of Oliver, U.S. Pat. No. 4,111,261, the lower extension 162 of a mandrel 38 is integral with the piston 180 and contained within a cylinder 36. An upper mandrel extension 164 which is connected to the upper end of the lower extension 162 of the mandrel extends upward through the cylinder 36 and terminates is a valve 210 through which high pressure fluids may be added to the well during servicing of the well. The resultant high structure remains on the well during the servicing.
The height of the structure leads to high bending and twisting loads on the wellhead when acidizing and fracturing services are being performed. This can lead to damage to the wellhead and problems with removal of the isolation tool.
It is desirable to have an isolation tool configuration which will protect the mandrel when it is being inserted in the wellhead, protect the personnel and environment from the dangers of a blowout if there is a catastrophic leak in the mandrel packing and also have the protective container and the insertion mechanism removable from the wellhead once the mandrel has been installed in order to have in place a low profile isolation tool.
The invention in one aspect may be viewed as an insertion apparatus for protecting and inserting a mandrel through the low pressure wellhead and associated equipment. The insertion apparatus attaches to the wellhead in a pressure sealing way and remains in place while the mandrel is being inserted through the wellhead and sealing in the tubing with one of the many available sealing nipples. The mandrel is locked in place and then the insertion apparatus is taken off.
The well servicing equipment is then attached and the servicing done. After the servicing, the insertion apparatus is sealed to the wellhead and the mandrel extracted. The wellhead valves are closed and the insertion apparatus removed.
In one aspect the invention comprises an improvement to a wellhead isolation tool having a mandrel and a packing which are protected and pressure sealed from the surroundings during insertion of the mandrel in the wellhead by the insertion system of the wellhead isolation tool.
In a second aspect the invention comprises an improvement to a wellhead isolation tool having a mandrel and a packing and the insertion and pressure sealing portion of the isolation tool being removable from the wellhead after insertion of the mandrel by the isolation tool.
More specifically there is provided a wellhead isolation tool for attachment to a wellhead, the wellhead including tubing, the wellhead isolation tool comprising:
a pressure tight cylindrical unit having a cylindrical bore; PA1 a rod forcibly reciprocatable within the cylindrical bore of the unit, the rod having a lower end and a latch attached to the lower end of the rod; PA1 a mandrel attachable onto and detachable from the latch, the mandrel having a sealing nipple; PA1 an isolation valve attachable to the cylindrical unit; PA1 means for attaching the wellhead isolation tool to the wellhead; PA1 the cylindrical unit, the isolation valve, and the attaching means defining a sealed bore for the mandrel and rod to move within; PA1 and the mandrel being movable from a first position out of the wellhead to a second position with the sealing nipple sealed against the tubing. PA1 The mandrel is preferably locked within the wellhead, using a locking spool separate from the attaching means and from the isolation valve. Valves are preferably also provided to equalize pressure across the sealing nipple while the mandrel is lowered into the wellhead. PA1 In another aspect of the invention there is provided a method of isolating a wellhead from high pressures, the wellhead having a wellhead valve which is initially closed and the wellhead having well tubing, the method comprising: PA1 inserting a mandrel into a sealed wellhead isolation tool, the mandrel having a sealing nipple on its lower end, the wellhead isolation tool having a cylindrical sealed hydraulic means for receiving and reciprocatably moving the mandrel, an isolation valve attached to the cylindrical sealed hydraulic means and means for attachment of the wellhead isolation tool to the wellhead; PA1 attaching the wellhead isolation tool to the wellhead; PA1 opening the wellhead valve; PA1 inserting the mandrel into the wellhead with the sealing nipple sealed against the tubing; PA1 closing the isolation valve; and PA1 removing the cylindrical sealed hydraulic means from the isolation valve.